Method of bonding a tungsten member to a backing member



March 15, 1949.

E. I. LARSEN ETAL METHOD OF BONDING A TUNGSTEN MEMBER TO A BACKING MEMBER' Filed April 4, 1944 30 i. i im 5''! iil 2/ Illmm r I: 4

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I METHOD OF BONDING A TUNGSTEN MEMBER TO A BACKING MEMBER Earl I. Larsen and Earl F. Swazy, Indianapolis, Ind., asllgnorl to P. B.- Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Application April 4, 1944, Serial No. 529,533

' 3 Claims. 1 I The present invention relates to composite articles and methods of making the same. More particularly the invention relates to the production of multi-metallic articles such as electrical contact elements, x-ray targets, spark gap electrodes, spark plug electrodes, welding electrodes, etc., in which one of the component members is formed of tungsten, and the other component is a material having physical properties different from those of tungsten.

It has been found that the chief cause of the failure or unsatisfactory performance of multimetallic articles of the type mentioned above is due to distortion, warping or other surface changes thereof which sometimes produce cracks.

fissures and the accelerated deterioration of these .4

articles and which, in turn, are usually due to the difference in the coeflicient of thermal expension of the tungsten and the dissimilar material or materials.

Among the objects of this invention are: to avoid the above disadvantages and causes of failure; to provide a method of and means for producing composite metal articles free from incipient points of weakness and unrelieved stresses and strains which would cause accelerated deterioration of such articles; and to provide multimetallic structures of increased strength and durability.

Other'objects and advantages of this invention and details of manufacture and construction thereof will in part be obvious and will in part appear from the following description of preferred embodiments of the same when read in conjunction with the accompanying drawings,-

Compositions containing tungsten, nickel and molybdenum Compositions containing tungsten, nickel and copper Tungsten, so to 95% Nickel, 10 to 2.57 Copper, 10 to 2.5 0

Tungsten, 60 to 95% Nickel, 20 to 2.5% Molybdenum, 20 to 2.5%

It is within the scope of the invention to replace any desired proportion of either the copper or the molybdenum by the addition of gold. Furthermore, small percentages, i. e., up to about 1%. of manganese, cobalt, or iron may be incorporated in the sintered composition.

The following are typical examples of sintered backing compositions according to this invention:

Figures 3 through 6 are illustrative of a number of different embodiments of the invention.

The present invention relates especially to and has particular utility in the production of articles of the type mentioned above which may require relatively large and thin contact facing discs formed of tungsten. The invention contemplates overcoming the difllculties in the fabrication and operation of contact elements and X-ray targets of which tungsten is a constituent part of the contact facing by providing a special type of sintered backing composition forthe tungsten contact facing; or, in some cases, by providing the special backing composition between the tung- (I) (H) Percent Percent Tungsten 90 Tungsten 90 Molybdenum 5 Copper 4 Nickel 5 Nickel 6 (III) (IV) Tungsten 90 Tungsten 85 40 Copper 5 Nickel 8 Nickel 5 Copper 8 Percent Tungsten 94 Nickel 3 Molybdenum 3 In a typical method of carrying out this invention, suitable for example for making X-ray tare d shrinkage may be as much as about 20%,the pressed discs were placed in a carbon boat on a thin layer of Alundum sand with a piece of Alun-= dum slab between the sand and the bottom of the carbon boat, and sand was sprinkled over the Alundum to facilitate movement for the.

shrinkage during sinterlng. The carbon boat, with Alundvrn, sand, and the discs was placed in to a sintering furnace and sumclent heat was ap= plied to insure complete volatilization of t e binder material, but not enough to exceed a black heat (about 500 C.) After the binder material had burned, the boat was gradually advanced into the heat, and after centering the discs in the hottest section, time was allowed for the boat to reach the sintering temperature which was about 1500 C. After a heating period of Eli minutes, the boat was pulled directly into the cooler. Tests and measurements indicated that the linear shrinkage during sintering was to 19%, the hardness was 30 to 38 Rockwell C, and the density of the sintered discs was about 17.3 gms./cc.

Generally, the sintering mmperature should be high enough to create a molten phase of the elements molybdenum-nickel (in the case or compositions (I) and (V) above), or coppernickel (in the case of compositions (11), (ill) and (IV) above), which results in a thorough difiusion of the two metals within each other with the formation or a eutectic alloy in certain instances. This, molten alloy dissolves a portion of the powdered tungsten particles and exudes either the molybdenum-nickel or the coppernickel phase, and-it is this exuded molten phase which faoilitatesthe subsequent brazing of the tungsten base composition to the tungsten discs, as described in more detail below.

lifter sinterlng as described, the discs were machined, and then brazed. According to this invention, advantage is derived from the lower melting point of the exuded nickel-molybdenum or nickel-copper alloy as well as from the phe nomena involved in the fusion and freezing thereof, in order to effect the integral union of the alloy with the tungsten facing material. liquid phase (nickel-molybdenum or copper molybdenum) which exudes during the slntering isused as the chief constituent the bracing medium. The brazing is reflected by heating tungsten disc in intimate contact with the tung= sten base composition at a temperature adapted to insure suiilclent fluidity of the liquid phase, which he Example I was about 148W C. .l-lccor ing to a preferred. procedure, the tungsten base Referring now to the drawings, Figure 1 shows a tungsten X-ray target ill which, as shown, is embedded in the tungsten base composition H, the latter being brazed, welded or otherwise secured to the supporting member l3 which may position is brazed or welded to a further backing shape exemplified in the embodiment shown as composition is placed upon and in direct con= tact with the upper surface of the tungsten disc; thus upon heating, the exuded molten phase of the backing member will be deposited by fusion upon and into the surface pores of the tungsten member, and during the freezing of the molten phase, any tungsten grains or particles which have entered into solution with the molten phase are precipitated out, thus resulting in a gradual duplex structure at the brazed joint in which there is a progressive enrichment of tungsten particles from top to bottom or the joint. lrre== spectlve of the particular mechanism of fusion and solidification, micrographic examination of the brazed joint obtained by the process and ma terials of Example I showed that the molten phase of the tungsten base composition had dill-=- fused into the crystal structure of the tungsten disc and had formed a matrix cementing the two together. I

a rivet 32 made of steel or any other desired me tallic material.

The modification of the invention which is shown in Figure l represents a side view of a contact arm consisting of the tungsten contact facing disc Ml which is brazed directly to the backing material represented here as the contact arm ll.

Figure 5 is a sectional View through a welding electrode consisting of the tungsten facing disc til, which is brazed to the tungsten base composition til, the latter being screw-threaded into the body of the welding electrode 52. A water tube 53 is provided to cool the welding tip of the electrode member.

l igure6is a side view partly in section of a spark plug electrode, illustrating a further embodiment of the invention. The tungsten sparking member is represented at till and as shown, it is integrally united at 69 with the tungsten base composition (52 which in turn is united by screw threads 68 with the niclrel rod 6 3.

it will be understood that discs, plates or other shapes, or iaclngs of metallic tungsten could be secured to the backing member or members by a brazing or welding procedure different from the above embodiments, and that the invention is not limited to the use of the particular brazing pro= cedure described, but the invention is in tended to be covered oadly within the and scope of the appended claims.

What is claimed is:

ii, The method of reducing distortion in a corn-= posite metal article or which one component member consists of tungsten predominating proportions, which comprises contacting said member with a leaching member or" a composh tion containing about so to tungsten, about 2.5 to 29% nickel and the remainder consisting of a third metal selected from utleast one oi the elements molybdenum and copper, and heatsaid members to a temperature sutrlclently highv as to create a molten phase of nickel and the third metal so that said molten phase exudes from said composition and unites said members by fusion,

2. The method of brazing a metallic material comprising a predominating proportion of tune sten to a metallic material having a coefllcient of thermal expansion substantially different from that of tungsten, which comprises int'erposlng between said two materials a composition con 5 nickel and the third metal so that said molten phase exudes from said composition and fuses with said materials.

3. The method of brazing a tungsten facing metal to a backing member which comprises providing a backing member having a coefllcient of thermal expansion close to that of said facing metal and composed of a ternary composition of tungsten, nickel and the remainder at least one of the elements molybdenum and copper, l0

heating said member to a sintering temperature at which there exudes a binary liquid phase of mid nickel and one of said third elements, heating the said facing metal in intimate contact with the said backing member to a temperature adapted to insure sumcient fluidity of said exuded binary phase whereby saidexuded phase will be deposited by fusion upon and into the surface pores of the said facing metal and particles of said facing metal will enter into solution with said exuded phase, and cooling the combination 6 to securely bond thecsaid facing metal to said backing member.

EARL I. LARSEN. EARL F. SWAZY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,469,043 Laise Sept. 25, 1923 1,625,427 Rentschler Apr. 19, 1927 2,060,959 'Terry Nov. 17, 1936 2,096,924 Schwatzkopf Oct. 26, 1937 2,183,359 Smithells Dec. 12, 1939 2,186,319 Bilton Jan. 9, 1940 2,191,460 Fisher Feb. 27, 1940 2,232,176 Guthrie Feb. 18, 1941 2,234,834 Scott Mar. 11, 1941 2,300,286 Gwyn 1-..-.. Oct. 27, 1942 

